181 research outputs found

    Faster all-pairs shortest paths via circuit complexity

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    We present a new randomized method for computing the min-plus product (a.k.a., tropical product) of two n×nn \times n matrices, yielding a faster algorithm for solving the all-pairs shortest path problem (APSP) in dense nn-node directed graphs with arbitrary edge weights. On the real RAM, where additions and comparisons of reals are unit cost (but all other operations have typical logarithmic cost), the algorithm runs in time n32Ω(log⁥n)1/2\frac{n^3}{2^{\Omega(\log n)^{1/2}}} and is correct with high probability. On the word RAM, the algorithm runs in n3/2Ω(log⁥n)1/2+n2+o(1)log⁥Mn^3/2^{\Omega(\log n)^{1/2}} + n^{2+o(1)}\log M time for edge weights in ([0,M]∩Z)âˆȘ{∞}([0,M] \cap {\mathbb Z})\cup\{\infty\}. Prior algorithms used either n3/(log⁥cn)n^3/(\log^c n) time for various c≀2c \leq 2, or O(MαnÎČ)O(M^{\alpha}n^{\beta}) time for various α>0\alpha > 0 and ÎČ>2\beta > 2. The new algorithm applies a tool from circuit complexity, namely the Razborov-Smolensky polynomials for approximately representing AC0[p]{\sf AC}^0[p] circuits, to efficiently reduce a matrix product over the (min⁥,+)(\min,+) algebra to a relatively small number of rectangular matrix products over F2{\mathbb F}_2, each of which are computable using a particularly efficient method due to Coppersmith. We also give a deterministic version of the algorithm running in n3/2log⁥Ύnn^3/2^{\log^{\delta} n} time for some ÎŽ>0\delta > 0, which utilizes the Yao-Beigel-Tarui translation of AC0[m]{\sf AC}^0[m] circuits into "nice" depth-two circuits.Comment: 24 pages. Updated version now has slightly faster running time. To appear in ACM Symposium on Theory of Computing (STOC), 201

    Rituximab Not Effective for Hearing Loss in Cogan’s Syndrome

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    Importance. Rituximab was not effective in ameliorating the hearing loss in a patient with atypical Cogan’s syndrome. Observations. We report the case of a patient who developed acute bilateral uveitis and sensorineural hearing loss. A diagnosis of atypical Cogan’s syndrome was made. The patient’s hearing loss did not improve despite high dose steroids and azathioprine. Rituximab was administered given a recent report of its efficacy in a patient with refractory disease; however, our patient’s hearing loss did not improve. Conclusion. Hearing loss in Cogan’s syndrome is difficult to treat. Though rituximab was ineffective in our case, earlier administration in the disease course could be effective for future patients

    An Ecological Approach to Understanding Program Management Practices for Food Pantries in Rural Communities

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    This qualitative study was conducted in Mississippi, a state comprised of 82 counties, many of which are rural and highly impoverished. To gain a greater understanding of the food needs of residents from across the state, a representative sample of food pantries from each region of the state was identified. For this project, researchers with the Mississippi Food Insecurity Project formed a partnership with the Mississippi Food Network to interview partner pantries across the state. Interviews were conducted with food pantry managers and volunteers to examine various issues, challenges, and successes related to their operations. All interviews were transcribed and coded using a systematic analysis of codes to generate major themes related to pantry management protocols. Using an ecological framework, our study yielded five major areas of consideration for optimal pantry management: volunteer recruitment, operating and control systems, patron needs, collaboration, and advocacy

    Interpreting the Biological Effects of Protons as a Function of Physical Quantity: Linear Energy Transfer or Microdosimetric Lineal Energy Spectrum?

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    The choice of appropriate physical quantities to characterize the biological effects of ionizing radiation has evolved over time coupled with advances in scientific understanding. The basic hypothesis in radiation dosimetry is that the energy deposited by ionizing radiation initiates all the consequences of exposure in a biological sample (e.g., DNA damage, reproductive cell death). Physical quantities defined to characterize energy deposition have included dose, a measure of the mean energy imparted per unit mass of the target, and linear energy transfer (LET), a measure of the mean energy deposition per unit distance that charged particles traverse in a medium. The primary advantage of using the dose and LET physical system is its relative simplicity, especially for presenting and recording results. Inclusion of additional information such as the energy spectrum of charged particles renders this approach adequate to describe the biological effects of large dose levels from homogeneous sources. The primary disadvantage of this system is that it does not provide a unique description of the stochastic nature of radiation interactions. We and others have used dose-averaged LET (LE

    Young adult outcomes associated with teen pregnancy among high-risk girls in a randomized controlled trial of Multidimensional Treatment Foster Care

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    Teen pregnancy is associated with a host of deleterious outcomes for girls, such as drug use and poor parenting. Thus, reducing teen pregnancy rates could improve long-term developmental outcomes for girls, including adjustment during young adulthood. Based on the positive effects of Multidimensional Treatment Foster Care (MTFC) relative to group care (GC) in a study of adolescent girls (significantly fewer pregnancies reported in the 2-year follow-up for MTFC girls), the present study followed this sample into young adulthood (approximately 7 years post-baseline) to examine the effects of adolescent pregnancy on young adult substance use and pregnancy-related outcomes. All participants were randomly assigned to MTFC (N = 81) or GC (N = 85) as adolescents as part of a randomized controlled trial (RCT). Results from logistic regression analyses indicated that becoming pregnant during the 2-year follow-up was significantly related to illicit drug use, miscarriage from a new pregnancy, and child welfare involvement 7 years post-baseline. In addition, baseline marijuana use predicted marijuana use at 7 years post-baseline. © 2013 Copyright Taylor and Francis Group, LLC

    Structure of Complement Component C2a: Implications for Convertase Formation and Substrate Binding

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    SummaryC2a provides the catalytic center to the convertase complexes of the classical and lectin-binding pathways of complement activation. We determined two crystal structures of full-length C2a, with and without a pseudo ligand bound. Both structures reveal a near-active conformation of the catalytic center of the serine protease domains, while the von Willebrand factor A-type domains display an intermediate activation state of helix α7 with an open, activated metal-ion-dependent adhesion site. The open adhesion site likely serves to enhance the affinity for the ligand C4b, similar to “inside-out” signaling in integrins. Surprisingly, the N-terminal residues of C2a are buried in a crevice near helix α7, indicative of a structural switch between C2 and C2a. Extended loops on the protease domain possibly envelop the protruding anaphylatoxin domain of the substrate C3. Together with a putative substrate-induced completion of the oxyanion hole, this may contribute to the high substrate specificity of the convertases
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